John Calvin Commentary Titus 1:14

"not giving heed to Jewish fables, and commandments of men who turn away from the truth." — Titus 1:14 (ASV)

And may not listen to Jewish fables. He now shows in what “sound faith” consists—when it is not corrupted by any “fables.” But in guarding against this danger, he prescribes this remedy: not to listen to them.

For God desires us to be so attentive to His word that there will be no opening for trivial matters. Indeed, once the truth of God has gained admission, all that can be brought against it will be so unappealing that it will not attract our minds. Therefore, if we wish to preserve the faith uncontaminated, let us learn carefully to restrain our senses, so that they do not surrender to strange inventions; for as soon as anyone begins to listen to fables, they will lose the purity of faith.

He calls all trivial inventions “fables,” or, as we would say, “trivialities”; for what he immediately adds about “the commandments of men” has the same meaning. And he calls those people enemies of the truth who, not satisfied with the pure doctrine of Christ, mix their own foolish ideas with it; for all that people devise on their own ought to be considered “fictitious.”

He attributes this vice chiefly to the Jews because, under the pretense of the divine law, they introduced superstitious ceremonies. The Gentiles, aware that they had been miserably deceived throughout their entire lives, more easily renounced their former way of life; while the Jews, having been educated in the true religion, obstinately defended the ceremonies to which they were accustomed and could not be convinced that the Law had been abrogated.

In this way, they disturbed all churches because as soon as the gospel began to appear anywhere, they did not cease to corrupt its purity by mixing it with their leaven. Accordingly, Paul not only forbids them, in general terms, to stray from sound doctrine, but also points out, as if with his finger, the present evil that needed to be remedied, so that they might be on their guard against it.